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Can a sonic boom arrive before the source?
I'm on the ground, a fast jet flies from very near to the ground, I hear the sonic boom soon, but after the plane passes my point, right?
The real question I'm trying to solve is this:
I just heard an explosion-like sound, and then heard a jet pass. So this means there was an explosion. Am I correct?
One thing I doubt is that the "normal" sounds I heard after could also be "lagged", so it might have confused me about the timing, but I think that wouldn't make a big difference.

If you were standing in a road and a car travelling faster than the speed of sound came at you, it would hit you before you heard it. Perspective may change this when you add in altitude and curvature of the earth. Unless you are talking about military aircraft I doubt what you heard was a sonic boom.

Yes it's supposed to be a military aircraft. I was standing home then a sound wave hit, like it opened the window. then (a few seconds later) a plane pass from very close with a very loud sound. I always assumed that the sonic boom would come after the plane starts to get away from me. Isn't it right?

I guess they are F-16 jets, well I'm not sure about the altitude but they were flying really low, but it was pretty near to the minimum acceptable (well, possible) height.

For all I know, you could have heard the sound of the jet engine. They don't allow planes flying at supersonic speed over the US unless you are outside of it, then it might depend of what country you are in.

You cannot hear something (sonic boom or engine sound) "before" something moving at or above the speed of sound as reached a position abeam your location, if the aircraft flies in linear trajectory. However if the aircraft follows a curve it is possible to hear the sound before seeing the aircraft and think the aircraft was further at the time your heard the sound (but its a an illusion).

The airplane could break the sound barrier, then slow down again, be overtaken by its shockwave and follow it, right? (I guess that's just a special-case of a non-linear trajectory already mentioned by @mins , anyway.)

If you were at your house and you heard a sonic boom, someone broke a law/FAA regulation (assuming USA). If what you did hear was a sonic boom, followed by seeing and hearing a jet fly by at low altitude, there would have been 2 planes - you heard, but never saw, the first one, then, alerted by the sound, you looked up and saw & heard the second one.

My guess is that there were two aircraft exceeding the speed of sound. You didn't see the first one, but its sonic boom was what caused you to look in the sky, and you then saw--and later heard--the second aircraft. (Apologies to @FreeMan. I didn't fully read your comment before writing my own.)

Did the OP say that he ever saw the plane? Seems like he describes exactly how a supersonic flyby would sound. 1) aircraft passes overhead before any sound 2) Shock wave would arrive first 3) followed by the sound of the jet. Only one plane required. It may not have occurred in the US and, legal or not, I've heard sonic booms at my home twice. Once there were four in quick succession at the wee hours of the morning. I say wee hours because I nearly peed myself they were so loud.

I'm sorry if this is prying, but I'm curious: do you by chance live in Turkey?

@yshavit yes, this is from the "coup attempt". :) TomMcW; no I never saw the planes, so you say that a sonic boom can arrive -1 or 2- seconds before the "normal" sound waves?

@halil You can never hear the actual jet before the sonic boom arrives. What you describe is exactly how you would hear a supersonic jet. Source: I grew up near an airbase.

Assuming the aircraft you saw was traveling in a straight line, then the sonic boom you heard (assuming it was a sonic boom) could not have been generated from that same aircraft.  This is because the sonic boom is experienced at an angle back from the flight path of the aircraft.

Many aircraft which are capable of generating sonic booms also happen to fly in groups.  Fighter jets are a good example of this.  Fighter jets often train in groups of more than one aircraft.
It's possible you may have heard a sonic boom from another aircraft at a higher altitude which you did not see, then you later saw a new aircraft.  This is actually very likely, because sonic booms are much more common at high altitude.  The atmospheric conditions for creating sonic booms are favorable at high altitude.  This is because the speed of sound is much lower at high altitude compered to the speed of sound at low altitude.  It is difficult to see military aircraft at high altitude against a blue sky background because the military intentionally paints the skin of the aircraft in a grey color to make it difficult to see against a blue sky.  So without a con trail you likely did not see the fighter jet which was flying at high altitude.
Other commenters asserted supersonic flight is not allowed inside the US, but this is not entirely correct.  Many restricted airspaces in the US allow supersonic flight.  The restrictions on supersonic flight are generally put in place to balance the concern of noise pollution for the population.  Some MOA (military operating area) also allow supersonic flight, although usually only at high altitude.  Some areas of the eastern US which allow supersonic flight require the pilots to fill out a log stating supersonic flight occurred.  However, supersonic flight is easy to do accidentally in many fighter aircraft.  The pilot may not realize he was supersonic until reviewing the tapes after the flight.  Most airspaces allowing supersonic flight are over sparsely populated deserts of the western US.
Picture credit to Wikipedia

Thanks for your explanation. Nothing happened that night was assumed to be compliant with the law. And from what we heard, there were 2 jets, but I thought they were flying separately. But you are right, it can be the two of them passing consecutively. Unfortunately I have (or anyone has) too little information to confirm any of this :) But still, thanks.

Military jets often fly at night with their exterior lights set to only emit in the range which is visible to someone wearing infrared googles.  That way the pilots can see each other, but the enemy cannot see them without NVG equipment.  Such a scenario is another reason you might not have seen all of the aircraft.

Wouldn't the sonic boom get out in front as the airplane slows down to subsonic flight (especially if done rapidly)?

@Lnafziger this might be theoretically possible, but in practice the aircraft would not be able to slow down sufficiently during the time the last sonic boom emission travels to the listener.  Fast moving aircraft have a great deal of momentum, and deceleration happens slowly.  Even if the plane changed speed from 800 knots to 0 knots instantly, the sound would reach the observer in just a couple seconds.  And the aircraft would still be in view.  A better question is "could the aircraft turn around 180 deg fast enough?"  I don't know if it could turn fast enough, but maybe.

re "other commenters asserted supersonic flight is not allowed inside the US..." -- the OP confirmed in the comments above that they live in Turkey, and this was part of the recent failed coup. I would hazard a guess that a fighter pilot who is involved in a violent overthrow of their country's government is not concerned about a bit of noise pollution. :)

@yshavit Yea he has other things to worry about now

I live in Los Angeles, and we did get sonic booms here occasionally related to some of the military operations such as at Edwards and Vandenberg. When the space shuttle was still operating, we'd get that sonic boom if it was landing at Edwards. Also, when Lockheed Skunkworks was in Burbank, I remember the occasional boom sound consistent with a sonic boom. I don't recall hearing any since Skunkworks moved out to Palmdale and the shuttle was retired however. BUT one other thing... (next comment)

When NASA retired the shuttle, they gave them to museums. We have Endeavour here at the California Science Center. They flew it in piggyback on the 747 to LAX. On the way in, the cavitation noise was crazy, and had a boom-like quality, though the aircraft was subsonic. It was not like the "sharp" boom, more of a big, longer, rolling/rumbling boom. And in this case preceding the aircraft as it was flying subsonic. QUESTION FOR ANYONE: (Was the boom somehow related to transonic flows of the piggybacked shuttle/747 combo? And not cavitation as I have assumed?)


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VORTAC symbol over KMOT airport - is the small dot the center?
I am looking at KMOT and I see a little dot over the airport symbol, is that the center of the VORTAC?

When you say "over" the airport symbol, do you mean the dot inside the blue circle and between the west ends of the runways, or the dot inside the star above the blue circle?

Hello Pondlife, I mean the dot inside the airport, I added picture for clarification.

Yes.  That small dot is the approx.  location of the VOR/VOR-DME/VORTAC on an airfield, should the airfield be so equipped.

The dot in the center of the star means that there is a rotating beacon available on the airport from sunset to sunrise.
See the FAA Aeronautical Chart Users Guide Page 8.

The actual center of the VORTAC is the small dot between the runways:

Which you can find the description of in the chart users guide on page 8 as well:

It says the star represents the rotating beacon, I am wondering about the small dot, I want to know where to gauge the center for the VORTAC

@Jeff See the edit

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What are the advantages of squawking 7700?
I was reading this question about how do pilots send distress signals in emergency scenarios, and that got me thinking...
In voretaq7's answer, he states that there are three ways to send distress signals, one of them is by the aircraft's transponder

Three transponder codes are reserved for unusual/emergency situations:
   - 7700 for general emergencies.
   - 7600 for loss of communication    (radio failure).
   -  7500 for hijacking or other unlawful    interference.

I can understand the reason to squawk both 7500 and 7600 in the appropriate situation, but I'm failing to understand why squawk 7700 in an emergency scenario.
So that's what I'm thinking:

In case of a hijack, the ability to squawk 7500 to silent alert the ATC of the situation, without the hijacker knowing, is an advantage.
In case of a radio failure, where you can't alert the ATC over the radio, the ability to squawk 7600 and make them aware of your situation, is an advantage.
In case of emergency, where the pilots are trying to handle a lot of things (high workload scenario), to stop everything to configure the aircraft's transponder, when they are communicating with the ATC by radio, doesn't seem like a good thing to do.

So, finally, here are my questions:

Is it common for pilots to squawk 7700 in emergency scenarios?
What are the advantages, for the pilots, to squawk 7700 in emergencies situations?

changing to 7700 is probably just a single button press.

There's already a partial answer to this: http://aviation.stackexchange.com/questions/2163/how-do-commercial-pilots-send-distress-signals

There are a few examples in aviation where an aircraft has been in trouble, but due to language barriers has failed to correctly make the seriousness of this situation known to air traffic control. Look up Avianca Flight 52 as an example. They were low on fuel, and eventually crashed due to fuel starvation, with ATC not being aware how bad their situation was. Squawking 7700 would have saved lives in this case.

Avianca Flight 52

Even if you are in communication with ATC and they request you to squawk 7700, which they most likely will, you fly the aircraft first. If I was really busy, I would probably just respond 'Standby'. If I was super busy and I am about to die if I don't get this right, I wouldn't even respond. Only when I have sorted myself out, will I then think about changing the squawk. To be frank, I wouldn't even bother replying back to ATC following the standby since they will know quicker than I can call them. Aviate, navigate, communicate. People have died because the pilot didn't do those things.

Isn't it bad that everyone (including possible hijacker) knows squawking 7500 means a hijacker is on board? In this case the silent-signal isn't so silent.

Very good answers, all. I am a Private Pilot and I agree with most of the answers here. If I have passengers on my flight, I tell the right-seater that in case of an emergency where I am incapacitated, he/she should input 7700 on the transponder and send out a distress call to a nearby ATC facility (which I also write down for them). The single engine planes I fly are very stable and if the pilot is incapacitated, a non-pilot can easily keep it flying until help "arrives" if necessary.

If you make a radio call, unless you are on 121.5 (or 243 military), then only the station you are talking to will initially know about the emergency. Initial calls should always be with the unit you are working with unless you are VFR.
If you squawk 7700, then all stations in transponder range, including possible airborne stations such as AWACS and SAR will know right away that you are in trouble, with position, altitude and possibly aircraft type and flight number.
If VFR, you might not be talking to anyone and may not have the frequencies of nearby units easily to hand.
Squawking 7700 is definitely a good thing.
You mentioned being busy.  The mantra drilled into everyone is "aviate, navigate, communicate".  In most circumstances, fly the plane, fly it where you want it to go, then tell someone about it.  Squawking 7700 will be one of the last actions carried out.

Nice informed answer.  I think that is exactly what these transponders are designed to do; to provide that 'extra' link.  A code, with no possibility of verbal garbling.  A Wide Area distress, with no need to try to initiate comms, possibly in eighteen different languages to dozens of busy people, who mostly don't expect, and won't be able to quickly understand why you are calling them out of the blue, haha. No seriously.

Thanks for your answer. If I squawk 7700, will it change how other nearby planes' instruments display me(radar, tcas, etc)?

@GabrielBrito On "normal" aircraft, no.  They have no equipment to interrogate other transponders apart from TCAS and AFAIK, regualr TCAS does not have any special symbology for displaying an aircraft squawking an urgency code.  AWACS, SAR etc will but I don't know details.

@Simon: What about ADS-B In/TIS–B displays? Unlike TCAS which is rigid and limited in its display, I am under the impression that there is basically no standardization of ADS-B/TIS-B displays. Therefore it is reasonably likely that some will choose to flag emergency aircraft to help VFR craft remain well clear. Sure, very few aircraft have them at the moment, but I suspect adoption will be reasonably rapid in glass cockpits since only a UAT or 1090ES transponder and a firmware upgrade are likely to be needed.

Interconnection of ATC systems is making your first point moot; ATCs especially at larger airports can flag an aircraft as under an emergency, and every other screen within radar range would know in seconds.

@Simon Are pilots expected to squawk 7700 when they are getting flight following or flying instrument under ATC control? I remember reading somewhere if you have an assigned squawk already, you're not expected to change it to 7700 unless specifically advised by ATC to do so

@lemonincider Reasoning purely logically, not about regulations, that would require that ATC be made aware of your emergency, which may be difficult in some situations. Of course ATC can request that an aircraft squawk 7700, and normally you'd be expected to keep using your assigned code, but if using one of the urgency codes is called for then getting ATC approval seems like an unnecessary step. Just imagine if you needed ATC approval to squawk 7600! Consequently, it makes sense that squawking 7700 falls under pilot authority. Of course, expect an interview once safely on the ground.

Aircraft squawking 7700 are getting a special indication (e.g highlighted, distinct colour, boxed) on Air Traffic Control (ATC) displays. This helps to identify the emergency aircraft not only to the air traffic controller who is controlling the airspace the aircraft is in, but also to controllers of other (nearby) airspaces. This helps to improve awareness and coordination within ATC.

In case of emergency, where the pilots are trying to handle a lot of things (high workload scenario), to stop everything to configure the aircraft's transponder, when they are communicating with the ATC by radio, doesn't seem like a good thing to do.

Typically communication to ATC, including setting the transponder to the general emergency code is of low priority during an emergency:

Aviate (make sure the aircraft keeps flying),
Navigate (make sure you know where you are going, don't fly into terrain while trouble shooting),
Communicate (let others know what you are doing)

Usually communication to ATC will be done using radio communications, but in some cases that may be difficult and setting 7700 will get the message that something is wrong across.
Often ATC will ask to squawk 7700 after the initial Mayday call to identify the aircraft not only to the controller you are talking to, but to other controllers responsible for nearby sectors as well. This aids in coordination between controllers and makes sure appropriate action can be taken by controllers of adjacent airspace / airports in preparation of the emergency aircraft's transition into their area of responsibility.
This video with ATC recordings of an emergency situation at Manchester airport shows you an example of ATC requesting an aircraft to squawk 7700 (at 2:00).

Thanks for your answer! Is it procedure to squawk 7700 after the initial Mayday call?

@GabrielBrito It think it is, it may vary from operator to operator, but I need to verify that. I am quite busy at the moment so I'll confirm next week.

@DeltaLima Did you ever look that up?

Because it gets highlighted immediately on ATC's equipment, without needing a lengthy radio message to describe the problem and identify one's position.

Without the radio message how can the ATC be aware of the nature of the emergency?

they can't. but ATC can see there's a problem and direct all the other planes out of the way

Good question about the radio message.  The first aim must be to make ATC aware of location, in case an actual forced landing occurs.  I should have said that a radio call should be placed too, but as it's away from the airfield the pilots would be forced to resolve the situation themselves, at least initially.

I've found a linked answer by the way - added as a comment to the question itself.

Concur with the other commenters that there are advantages to squawking 7700 at the appropriate time in the aviate, communicate, navigate steps. There is one situation not mentioned so far in which it might be especially important: when an emergency occurs after loss of communications for an IFR flight in IMC.
If an IFR flight loses communications while in VMC, the pilot is supposed to continue the flight under VFR and land as soon as practical (FAR 91.185). So if there is good weather out, and you set your transponder to 7600 and deviate from your IFR clearance by turning towards an airport at which you're going to land, ATC has a pretty good idea of what you're going to do and can act appropriately.
But what if you're in IMC? If you set your transponder to 7600 and proceed in accordance with the IFR lost-comm procedures, ATC will assume that you're going to continue to proceed in accordance with them (route assigned, vectored, expected, or filed; altitude highest of the minimum IFR altitude, expected altitude, or assigned altitude). But what if a different emergency occurs at that point and you need to deviate from that plan? If you then squawk 7700, ATC will know that you are deviating not because you're in VMC and continuing under VFR, but because you have an emergency and are exercising your PIC authority.
What good is that when ATC can't talk to you? I'd much rather ATC send emergency assistance to whatever airport I'm headed for or wherever I disappeared from their radar scope rather than waiting for me to call them on the ground. And it certainly helps that they're going to clear the skies of all traffic anywhere near me. Obviously if you have your hands full flying the plane then setting the transponder isn't a priority, but it does offer you considerable advantages if you have the time to do so.

As many others have mentioned here, if you squawk 7700 you will be highlighted on the ATC screens.  ATC will in turn clear traffic around you.  The advantages to this are obvious if you consider that you may be suffering controllability problems that are preventing you from being able to maintain heading or altitude.
Couple this with the fact you may also be having trouble communicating with ATC.  This may have nothing to do with radio trouble, as anyone can attest who has flown in a high density area (O'Hare, JFK, Atlanta, etc...) where the radio comms can be so clobbered that you can continually get stepped on.  Aviate, navigate, communicate and 7700 is communicating.
I have had in-flight emergencies that I didn't put 7700 in because I already had a discreet squawk and ATC answered immediately when I declared the emergency with my intentions to turn and descend.  Had they not responded, I would have put 7700 in and done what I needed to do to handle the emergency knowing that ATC would vector other traffic around me.

Having worked as both a controller and flight instructor, there is a lot of misinformation and outright guesses in here.
If you are already speaking with ATC and are on an assigned squawk code, do not change to 7700 unless you are explicitly instructed to. You have already been radar identified, they already know where you are. Most of the comments regarding your presentation on the radar display are wrong (e.g. it does not "light it up like a Christmas tree"). While it varies depending on the equipment and software, generally it will just add a small tag to the bottom of the data block that says something like EMER. That's not really necessary if you've already been radar identified, and as the OP said, pilots in an emergency situation have higher priorities than adjusting their transponders unnecessarily.
Now. If you are NOT already speaking with ATC, yes, this is a good idea. For the systems I am familiar with, a plane which was previously squawking 1200 that has changed to an emergency code (i.e. 7700) will force a larger datablock to appear on the display. This can aid identification (though it does not positively radar identify you for other reasons). Think of it as the transponder version of making a mayday call.
Another erroneous answer suggests that it can help other ATC facilities locate you. Sort of, but not in a particularly useful way. If anything, it adds work because those facilities are now calling the airspace that aircraft is in to verify it is being addressed; any shared identification will be handled appropriately by the controller and isn't something you need to worry about in an emergency situation.
I do agree with the person who suggested it'd be a good idea if one was already NORDO and needed to deviate from their clearance due to an emergency.
The overall principle to understand is that squawking 7700 is to aid ATC in identifying you. If you're already talking to them because of flight following or IFR flight, you're already identified - it's unnecessary. If you haven't been speaking with them, go for it.
Having worked several emergencies in my career, I did not have any instances where 7700 was used. There are the rare occasions when a controller may request it from a plane which is already on a discrete transponder code, but they are uncommon and related to ATC issues that a pilot wouldn't be aware of (for example, ease of identification in an area where conflicting control systems make point outs a hassle).
In any case, if you're already on an assigned squawk, keep it unless told otherwise. If you're on 1200 and don't already have ATC's attention, 7700 is one way to do so.

Transponder code 7700 immediately gets the attention of the controllers. They will know your location, direction of flight and altitude. This is extremely important in that they will convey this information to emergency services personnel who will be able to locate your (possible) crash site much faster. That is the primary reason to use this code. As a SAR mission pilot I can tell you it takes a very long time to call out an aircrew, launch and locate a downed aircraft. Aviate is always number one. If you do not maintain control of the aircraft is doesn't matter how long it takes to find it, you're still dead. If you are already on a discreet code and talking to a controller they will know where you are already and declaring an emergency will get you their full attention. Believe me you want the attention. If you are VFR at 3000 AGL and run out of fuel (happens a lot, really) squawking 7700 is faster than looking up a frequency and the conversation will not be of immediate help anyway. They will know someone is in trouble at x location, with x heading, with x descent rate and radar contact lost at x altitude. Help will be on the way.

A former tanker instructor, who I had at Flight Safety, emphasized that when a single pilot work load is high, and one is working an emergency, squawking 7700 gets to controller's attention, allows him to start planning, while the pilot can be focused on debugging the situation.  From a time and effort cost standpoint setting the transponder to 7700 takes less time than a radio call, and one can then ignore the multiple radio calls that may come in, until one has the bandwidth to handle the communications.
Years later, I had a panel fire at cruise, on a night IFR trip.  Conditions were largely VMC.  While working the fire, I squawked 7700.  The transponder got a couple of replies in, until I determined that I would kill the aircraft master. Minutes later the smoke had cleared, and I found my trusty brick aviation radio and called ATC.  They knew something had happened, as they saw 7700, and then they lost my secondary radar return.
They knew something was happening, and cleared traffic in my vicinity and particularly below me.  When I came back on, using a handheld, I was ready to tell them all the stuff they needed to hear (nature of the situation, fuel and souls) and I continued to my (nearby) destination.  Aside from pumping down the gear and having no lights, the flight was uneventful from that point on.
I could not have had even a short interchange with ATC in the time it had taken to squawk 7700, and moments later shutdown the aircraft master.
To answer the OP questions:
-Is it common to use 7700?  Probably, but what is your definition of "common"?
-Advantages?
1. No need to talk, especially if at a time when talk is distracting or not possible.
2. If not talking with ATC, ATC (and TCAS) has immediate awareness that your aircraft has an issue, and knowledge of where you are.
3. Saves words, telling ATC you have an emergency.

When you squawk 7700 you have to use your brains and hands to do other things besides flying the plane and troubleshooting your emergency.  You also light up the controllers scope like a Christmas tree, which is very distracting, causing them to quickly assign you a discreet code, meaning that you will be tempted to move your hands, yet again, to something that doesn't matter.
Much easier than squawking is to simply declare an emergency on the radio frequency you are already monitoring.  If I need to literally move my hands to squawk emergency then I've probably given up on the FAR/AIMS anyway because I'm about to die.  IE, electrical failures effecting both radios probably caused by a dual engine fire affecting both generators.
"77, going to heaven"--your mileage may vary.

Thanks for your answer. What is FAR/AIMS? And why would you give it up?

@GabrielBrito Federal Aviation Regulations and Aeronautical Information Manual.

Spoken like a true single seater.  Setting this transponder code is what the co-pilot (or back-seater) is for (if you have one).

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When were the first jet engines used?
I read a book about WW2 1 and saw a couple of planes with a giant jet engine on top of them, e.g. the Heinkel He 162 Salamander.
I realize jet engines had to have been invented before WW2 for that kind of technology to be used, so when were the first aircraft jet engines around?
1 Aircraft of World War II: 300 of the World's Greatest Aircraft. Chris Chant.

You can find this book at barnes and nobles.

https://en.wikipedia.org/wiki/Jet_engine

The first aircraft jet engine was ground tested by Frank Whittle in April 1937. In September of the same year, Hans von Ohain (ground) tested his jet engine.
The first jet aircraft, He 178 flew in August 1939.

What are your references? Fact checking and further reading is nice.

See http://inventors.about.com/library/inventors/bljetengine.htm and http://cs.stanford.edu/people/eroberts/courses/ww2/projects/jet-airplanes/planes.html. This information is available in Wikipedia too (See the comment on the question by Simon).

From Wikipedia:

In 2010, based on the notion that Coandă invented the first jet, the
  centennial of the jet aircraft was celebrated in Romania.

This aircraft was built by Henri Coandă, he of the effect that the NOTAR helicopter is based on. It was part of an aviation exposition in Paris, in 1910. Claims that it has actually flown are disputed, but not everywhere in the world apparently. The engine was a 50 hp piston engine driving a cowled fan.


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Why don't turboprop planes have push engines that use thrust more effectively?

The Piaggo P-180 is one of the fastest private planes out there and uses the push system.

You may wish to read https://en.wikipedia.org/wiki/Pusher_configuration#Disadvantages which describes a number of engineering considerations for a pusher configuration.

@Ethan You might consider putting a little more detail in your questions.  A lot of the question you are writing look more like statements...  It's okay to restate your question (with a little more detail) in the body of the question.

Pusher engines do not generate more thrust; they are basically the same engines, but mounted in a different configuration. As pointed out by @JanHudec in the comments, this configuration can be more efficient since in a traditional puller configuration the air displaced by the propeller washes over the wings and fuselage, thus increasing drag.
There are several considerations, such as those set out in the reference already given by Greg Hewgill in comments.
However, the main reason why propeller pushers are not as used on commercial aircraft is safety. Consider an aircraft taking off. If the pusher engines are placed, as usual, at the rear of the A/C, then the propeller tips are rather close to the ground. Even if the propeller does not actually make contact, any debris present on the runway and lifted by the A/C can conceivably end up within the propeller disk. This would be, naturally, at about the worst phase of flight to lose power.
This is perhaps less of a concern on drones and small aircraft used in GA. The pilot (and owner) may choose to forego a bit of safety to obtain a more compact aircraft and where the pilot's field of view is not interfered with by the presence of a spinner disk.
Another point that can be considered is the fact that turboprop engines are generally used in commercial aircraft that require shorter take-off and landing distances, to connect to smaller airports that handle jets with difficulty or not at all. In this case, a pusher configuration that requires higher speeds and longer runways would not be appropriate. On the other hand, in a puller configuration some of the prop-wash can be used to generate further lift through the Coandă effect and decrease take-off distance.

Yes, pusher engines are more efficient, see this answer.

@JanHudec The OP used the expression "generate more thrust". The engines do not generate more thrust, it is used more efficiently. Not quite the same. ;-)

It is not quite the same indeed, because the propeller itself has the same efficiency, the difference being in drag around the fuselage and wings. It still needs to be clarified, because while OP used the expression “generate more thrusts” I doubt they were aware of the subtlety.

@JanHudec "It still needs to be clarified" - you are perhaps right, have added it at the beginning of the answer.

The Piaggio is certainly fast but I'm pretty sure the speed is due to the plane's overall sleek shape, smooth skin, and resultant low drag working together with the high-power turbine engines. I don't think the push prop design is any more efficient, though the Italian style is first class.

"The Italian style is first class" - I especially like the handlebar moustache!


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What happened to the blades in this picture?
Here is the picture

Source:(brians-travels.com)
This looks like a photoshopped picture, but I believe it isn't. Is this some kind of strange occurrence that occurs only with the human eye? The blade on the top looks bent downwards. I can't figure out what happened in this picture. And will your picture look like this every time you take a picture of a fast moving propeller?

This is more a digital photography question than an aviation one, but check out the top google results for 'propeller blade weird camera' to learn more about what's called a 'rolling shutter'.

That happens more since the global warming has started, therefore it must be a metal softening effect of higher temperature.

@mins it has to do with how fast the blades are spinning. Your not going to get much metal softening because the temperature has only went up 1.5 degrees. That does have a huge effect on crops and glaciers.

I don't think this question should be closed, there are enough people out there who do not know what a rolling shutter is, and might think prop blades bend in flight.

You should ask this picture on Photography.SE (if it hasn't been asked already), this really is a camera question not an airplane question.

@falstro Good point, makes me wish we could move this questions over to Photography.SE and still have it linked here...  Is that possible?

"strange occurrence that occurs only with the human eye" -  no. The human eye is good enough to not see this effect. This "strange occurrence" only happens with relatively inexpensive cameras. Specifically CMOS cameras (all consumer cameras, most prosumer cameras and a small number of pro cameras). If you were to take a picture with a CCD camera you wouldn't see this effect.

@Ethan Mins was joking. Hence the link to Wiki:Correlation does not imply causation.

At this point, over a year later, and with a perfectly reasonable answer, why are we trying to close this?  I admit it's questionable, I said so above, but you might as well just leave it now.

@JayCarr my suspicion is that, as we have done in other cases, if the answer is about aviation, we leave it open, else we close it.

This is a good, aviation related question, and appropriate for this SE. It just so happens that the answer has to do with camera mechanisms, not propeller design.

It's an artifact of how a digital camera downloads captures the image from the sensor called rolling shutter.
Essentially the image is captured a single line at a time and the fast moving propeller changes location between each line captured.
Wikipedia has a nice diagram showing what happens step by step:

On our sister site photography.SE has a question asking about it.

Another interesting exemple. And a another strange flying blade.

@mins That second one is just a standard aussie prop.

The same thing used to happen with the focal plane shutters in many film cameras, for the same reason -- I've seen photos from the 1940s with similar (if slightly less pronounced) apparently blade curvature.

This is a result of the way the camera shutters operate. Usually, the cameras don't capture images in the same way as human eye i.e. they don't take image of the whole scene simultaneously but rather 'scans' horizontally or vertically. In normal cases, this rolling shutter method is not a problem, but can cause issues when the object is moving at high speeds.
Quote from user FGK:

The plenomenon is due to Rolling shutter (also known as line scan) is a method of image acquisition in which each frame is recorded not from a snapshot of a single point in time, but rather by scanning across the frame either vertically or horizontally. In other words, not all parts of the image are recorded at exactly the same time, even though the whole frame is displayed at the same time during playback. This in contrast with global shutter in which the entire frame is exposed for the same time window. This produces predictable distortions of fast-moving objects or when the sensor captures rapid flashes of light.

Source: ephotozine.com
In other words, it is due to camera rather than the propeller blades themselves. The effect of a simulated rolling shutter on a spinning disc shown below:

"Rolling shutter effect" by Cmglee - Own work. Licensed under CC BY-SA 3.0 via Commons.

Note that this only affects digital cameras. Film cameras with physical shutters actually do capture the entire scene simultaneously.

The same happens on mechanical shutter, that's why traditional cameras had two flash synchronization modes, one by the "first curtain", one by the "rear curtain". The effect appears different, but is actually the same at a slower speed.

@reirab: For certain values of "simultaneously", which is to say "no, not really". Shutters do not move infinitely fast.

@reirab: Not all digital cameras, only CMOS cameras. CCD cameras capture the entire scene simultaneously (even more "simultaneously" than mechanical cameras)

@NathanTuggy I meant that film cameras (with physical shutters) don't scan the image pixel by pixel, not that the shutter is infinitely fast. While the shutter is open, the film is being exposed to the entire scene with a film camera, regardless of shutter speed. As far as I can tell, the link in mins' comment is just talking about whether the flash fires at the beginning of the exposure period or the end of it (which will determine where unlit objects in the scene appear vs. lit objects, like in the train/headlight example in the answer.)

@reirab: As the shutter(s) move across the film, you get effectively the same problem as here: the time between exposing different sides of the film is non-zero, so this problem can occur. (This principle is, I believe, also the same one that underlies the use of continuous film strips to capture a continuously viewable camera shot of a race's finish line, which shows in chronological order the finishers, despite only ever focusing a narrow vertical strip of light on the film at any one time.)

This is an effect produced by the digital camera that took the picture. The CMOS sensor "scans" the picture from one edge to another, possibly bottom to top in this example. Each line of the photo is taken at a slightly different time, and the prop moves fast enough that it moves a little bit in between each scan line. After the camera puts all the scan lines together into an image, you can get the effect you see here.
You can read more about this effect at Rolling shutter.


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Where can you find symbols (like these) that aren't on the legend?
I see a lot of these fan like symbols:

...on the Nav Canada Alaska Highway - Fort Nelson to Northway, 1:500,000 VFR Navigation Chart, but they're not anywhere on the map legend.
I presume they're marshland as they look a little similar to symbols I've seen on hiking maps, but I don't like assuming when making flight plans!..
Is there some universal reference somewhere that I don't know about? Are they indicating marshland, or are they something else entirely?


text:
What kind of dihedral would be most stable?
What kind of dihedral would be most stable?

An airplane with wing span x ft and whose dihedral begins from the root(attachment point to the fuselage) of the wings and whose wing tips are y ft above ground level.
An airplane with wing span x ft and its dihedral begins from the mid point of the wings from the wing root and its wing tips are y ft above ground level.
An airplane with wing span x ft and its dihedral begins at a distance 2/3 of each wing from the wing root and its wing tips are y ft above ground level.

Note: They are all low wing airplanes of equal size, power, weight, wing span, wing chord etc. Only the starting point of the dihedral and the angle of dihedral  vary.
I also believe a polyhedral wing will be most stable(everything being equal). Am I right?

More dihedral doesn't necessarily make an airplane more stable. With too much of it, oscillations like the Dutch roll are not damped any more.
A polyhedral wing can be chosen for different reasons than just stability: With the dihedral of the outer panels, any angle of attack change there is reduced by the cosine of the dihedral angle. This means that the lift curve slope is flatter there and stall happens later. This is a great way to combine an almost elliptical circulation distribution with pleasant stall characteristics, similar to a raked wingtip, but using dihedral instead of sweep!
For the stability derivatives of partial dihedral I recommend to turn to no other source than Sighard Hörner's Fluid Dynamic Lift. In chapter XIV it shows a plot of a rectangular wing with an aspect ratio of 6 where the location of the onset of the dihedraled wing fraction is plotted over the X axis. This data is taken from NACA's technical report 548:

Figure 13 from Chapter XIV of Fluid Dynamic Lift by Sighard Hoerner. Note that it plots the derivative of a derivative on the Y axis!
The $c_{l_{\beta}}$ curve can best be approximated by a sine curve. Note that the Y axis shows the $c_{l_{\beta}}$ and $c_{n_{\beta}}$ derivatives over changes in the dihedral angle $\Gamma$. To arrive at your expression with constant tip elevation for different dihedral onset locations, the curves need to be modified by dividing them by the cosine of the partial span (assuming the root is 0 and the tip is $\frac{\pi}{2}$). This would yield a constant value for $c_{l_{\beta}}$, so the dihedral onset is of secondary concern and the dihedral effect depends on the tip elevation. Note: This is valid only for rectangular planforms - as soon as taper is involved, things get more complicated. This PDF has more on effective dihedral of tapered wings.
NACA TR 548 supports your opinion:

The tests also showed that with dihedral only the outer one-fourth of
  each semispan, the dihedral effect was maintained to a much higher
  angle of attack than when the complete wing had dihedral.

I've been going through this for a long time now. The equations now makes sense. Thanks a lot. Pheew! (I'd like it to be simpler next time.

You'd right that the polyhedral wing would be most stable considering all other things being equal. One way to compare the effectiveness of the dihedral angles between two wings is to determine the equivalent dihedral angle- which is the dihedral angle of a constant dihedral wing with equivalent roll moment. The image below shows a curve relating the relative rolling moment of the wing as a function of the semi-span station.

Rolling moment as a function of semi-span station; image from rc-soar.com
So, a dihedral starting from mid-span would have 65% effectiveness compared to the one starting from root- i.e if the dihedral angle at semi-span is twice compared to that starting from the root, it will be 30% more effective.
Let's plug in some numbers and check this. Assuming that the 'y'- the height above root is 10 units for an equal semi span (quite unrealistic, I agree), the equivalent dihedral angle for various configurations can be given as below:

conventional- starting from root - 1
starting from semi-span - 1.3
starting from 66% of semi span - 1.2

As you can see, the polyhedral wing is most stable, when only the wing dihedral is considered. The best thing would be increasing the dihedral outwards. However, there are other things to consider here- like manufacturing isssues, locating engines, other things like wing sweep etc, which would make having a constant dihedral more cost-effective.

I believe that the polyhedral wing is stable but not the best because the wings are wide and too easy turn.  The good part is that it because of its width and mass, the wind will less likely be able to flip the wing and the plane over. Hopes this helps:)


text:
Why are fast passenger airplanes no longer produced?
Concorde was a fast aircraft, but no comparable aircraft is designed today by manufacturers.
What are the main reasons for manufacturers to prefer larger planes carrying more passengers rather than planes flying faster with a less passengers?


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Why are airports in Greece blurred and low res in Google Maps?
Why are airports in Greece blurred and low res in Google Maps?

See https://en.wikipedia.org/wiki/Satellite_map_images_with_missing_or_unclear_data

Regarding Bing not being blurred, I noticed that Google Earth has that exact image in its history from 3/25/2014. The images don't blur until 8 or so snapshots later on 6/29/2017, so it's possible later Bing imagery will be blurred.

The short answer seems to be that some countries have persuaded Google to blur out specific areas for "national security" reasons. Wikipedia has an article on it with some more (limited!) information. Interestingly, I couldn't find any official Google article on blurring in Maps, apart from some general references to Street View. And, as it turns out, Street View at ATH works as normal.
FWIW, it seems that Greece didn't persuade Microsoft to play along, because Bing Maps has much better images. That strongly suggests that the blurring is mostly security theater.
(By the way, I'm not saying that there are no security/privacy risks with Google Maps, Bing or other tools; it's just that some risks are more credible than others. security.SE would be a good place to ask more about that.)

During the "Cold War" when we only had paper maps, it was common to see a map with military areas, including airstrips, filled in white. Some countries would sketch in a few roads to try and disguise it. Those of us in the business recognised them from the shape straight away. So it's not a new thing, and not very effective anyway, because spy satellites etc.

Often already the companies google/bing etc. buy their material from has things blurred out. I once saw a youtube video trying to hunt down some mysteries about that, but I can't find it again.

Greece seem particularly funny about this stuff - I believe there have been a few cases of plane spotters being detained and such.

@RedSonja There's a row of satellite dish antennans somewhere on a mountain in Switzerland.  One is green and all the others are white.  One is military and all the others are civilian.  Which one is military is officially a state secret.

If one of the white ones is the military one, then the green one would be deception. But, nobody knows.

@DohnJoe It isn't the green one. I know that for sure. I was involved in installing a lot of extra security equipment on one of the white ones a few years ago. The others (including the green one) have all the same equipment. And everyone from my company who worked on that needed clearance.

Possibly, they were all intended to be painted green, but it was only discovered that somebody forgot to tell the painting company after n-1 of them had already been painted. Never attribute to conspiracy that which can be explained by a simple mistake!

@alephzero +1 for Hanlons razor, yet deception is a big part of military thinking, e.g. see false cockpits.

thank you for the answer, BTW that's really stupid, it's like advertising the airports that could be interesting targets

BT Tower is a 600FT+ tower in central London (Which even had a revolving restaurant)  and yet for decades it did not officially exist  -  State secrets can be weird

@GianlucaGhettini Enemy states already know it's used for military purposes. The goal is to prevent additional info from leaking out. Eg. type of equipment being used, datetime when they are used, etc.

In Greece, many domestic airports are (or were) either officially military airports, or they have an air force base attached which uses the airport.
Most other countries have entirely separate military bases. With Greek geography being so fragmented by mountains and islands though, and with such a shortage of flat land where runways can be built, it simply isn't practical for every island and every major area of habitation to have separate air force bases and civilian airports.  Combining the two makes absolute sense; but it does have the knock-on effect of requiring precautions to be taken for the civilian airport which would normally only apply to a military establishment.
Most Western countries wouldn't consider this level of military infrastructure to be necessary.  After the Turkish invasion of Cyprus in 1974 though, Greece is very aware of the vulnerability of its territory and the need to be able to rapidly deploy troops to defend that territory.  This is a major factor in Greece still requiring its young people to carry out national service.  The military are regularly visible in a way which might be normal for people in Northern Ireland or Israel, but not for people in much of the rest of the world.

It's pretty normal in many parts of the world for the military and civilian operations to share the same airfield, but the blurring of Google Maps doesn't happen in most countries. Even completely military airfields in the U.S. aren't blurred like that. You can go look at full-res maps of Edwards AFB or even Groom Lake on Google Maps if you want.

Wasn't it Greece who arrested a couple of game developers that observed its military installations for gameplay ideas (as THEY claimed!)?

@IMil Yes, Greece arrested 2 people that were in possession of 800 photos out of which 14 were of "classified" military installations. There are large signs saying "No photos!" on military bases but were ignored by the 2. They intentionally violate the law multiple times in 2011 and 2012.

I'm not saying they didn't photograph the bases; but surely if a base's secrecy is protected only by a sign - even a large one! - all competent spies already know it to the last inch. So, Greek action may have been completely legal, but IMHO hardly reasonable.

You are right, those bases' location is common knowledge to any interested state. However the photo prohibition has its uses. It aims at hiding additional info that can't be (or hasn't been) obtained by spy satellites for example.

The military airfield at Agrinio is not pixellated, and shows a lot of military aircraft in open storage at the eastern end and in the north-western corner.

@IMil Most military take that kind of thing seriously. Overhead images which you could get from the plane are one thing, but pictures at ground level will show you    accessible doors and windows, locations of cameras and alarms, where the guards patrol, whether fences are electrified, and so on.

Greece and Turkey are both parties to the Treaty on Open Skies. Both are entitled to receive aerial photography on each other's military activities, so the argument is moot.

@IMil, if I were a legitimate spy and wanted to get 14 high-res pictures of strategic locations of a military building, then disguising as some arbitrary guy with 800 harmless pics on my camera, and a harmless project to use them, would be exactly what I'd do...

This blurring or pixellation is quite common on military airfields in France, and I've even seen a few military airfields in the Netherlands pixellated.
Ironically, the fact that the area is pixellated is a huge red flag to 'there's something interesting here'!
It's not just airfields ... in France there is a place to the north of Paris which is pixellated, but it's in the suburbs (no airfield anywhere near!) see N 49.032600 E2.221700 ... it's a place called Tavernay.

Taverny was the HQ of air borne French nuclear power (https://en.wikipedia.org/wiki/Taverny_Air_Base). EDIT: was (until 2011)

Second sentence: see https://en.wikipedia.org/wiki/Streisand_effect

It's rather interesting how all of the famous "Area 51" in Nevada is 100% visible (and in high definition) on Google Maps. Makes you wonder if they really have nothing interesting in the surface, or if maybe the imagery is completely doctored.

@BrunoPhilipe - In the past, R-4808N (Area 51) was blurred on Google images. It was one of the first things I looked for as a kid when free online satellite imagery was coming into being.

@BrunoPhilipe How hard can it be to edit out a few, um... circles?

I was once getting a flight home from a small airport on the Greek mainland. We boarded the plane but take off was delayed for a long time. The pilot got on the intercom and apologised for the delay which was 'due to congestion in the Athens airspace'. We then saw a Nato AWACS take off from the runway we were waiting to use. Shortly after that two very smartly-dressed Greek Air Force officers walked out of the flight deck, got in a car and drove away.
Short answer: many Greek civilian airports have a military role as well.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Could sidesticks be linked?
A sidestick is spring-loaded to the centre position.
If there were servos under the stick, connected to the other side stick, so instead of being spring-loaded to centre, it was spring-loaded to the position of the opposite stick.
Then each pilot would get feedback on what the opposite pilot was doing, and the application of opposite stick actions could be prevented.
Is that feasible?
EDIT:
As this apparently is existing technology, then is there a reason Airbus is not using it?

Yes. Gulfstream G500 and G600 are the first civilian transport category aircraft to have active sidestick. However, instead of mechanical linkages between the two sticks, the side sticks are coupled electrically. It's much more prevalent in military aircraft.
Source: Aviation Week
So why isn't it being adopted by aircraft manufacturers with side stick controls (e.g. Airbus, Bombardier)? It pretty much all has to do with costs.

Active side sticks introduce more failure modes, such as jam and runaway, which would involve more software and mechanisms to detect and mitigate. These add complexity and introduce failure modes in their own rights, and they all add up to costs.
There is very little certification mandate to make side sticks active. All the objectives, such as stick force/G, stick force/V, have been met by passive side sticks. Airbus introduced envelope protection, most likely not because it was a nice-to-have, but because certifying the combination of lack of aerodynamic feedback on the inceptors and the choice of a pure C* control laws without speed stability demands it.
Certifying the first civilian active side stick is costly (but now it's been done by Gulfstream). There needs to be clear market reasons to do so. For Gulfstream, it may be (personal hypothesis) that the aircraft is being catered to the ultra-rich clientale and a novelty factor. For commercial aviation, the only reason I can think of is safety, which brings us to...
Would active side stick actually increase safety by leaps and bounds? This is a topic under research so the discussion has personal bias. On the A320 and A220, if both PF and CP side stick commands are detected, an aural "Dual Input" warning would sound. Obviously, AF447 crew ignored it. The final BEA accident report didn't mention the lack of tactile feedback as a reason for the crash; rather, crew confusion on stall recovery and lack of airspeed disagreement warning were highlighted.

Some good additional info about the active sticks in the brochure here: http://www.baesystems-ps.com/pdf/ais_mil_brochure.pdf

AF447 crew were not aware of the continued FO full aft stick input until too late. Indonesia Air Asia 8501 captain was not aware that the FO misunderstood his command, pulled the stick backwards, and averaged out the full forward stick input of the captain. An aural Dual Sound in a cockpit full of alarms and distractions was not enough in both cases.

@Koyovis Again, no recommendation/finding on side stick from NTSB/BEA in either case. This becomes subjective discussion.

Yes you may have a point there.

Yes! It is feasible and recommendable, because the force sensors in fingers may create the extra inputs not available when humans are not looking at their or each others hands in emergency situations.
What you describe is often applied in simulators, for instance in B737 sims where captain and F/O side column and wheel can be uncoupled:

Each column has its own Control Loading actuator.
Each actuator measures the pilot force, and applies suitable resistance forces.
The two actuators are normally linked in software, which can also unlink them.
The actuators are powered by electric motors, which are fail passive unlike the hydraulics of olden days which had to be protected from hard over failures.

So not only is it feasible, it is technology with a decades old experience in the aviation world. Photo above is from a sales brochure, the stick we made 25 years ago for a German car company for research in drive-by-wire. Electric motors with back-drivable gearing (not via geared wheels), the stick could still move when the motors were off. Two or more of them can be coupled in software.

"which are fail passive" - until a short circuit lets the motor run away to its stops.

@Sean Have you ever seen that huge array of circuit breakers in an airliner, that protect against short circuits? Point is, an unpowered electric motor is immediately unable to exert any force, and can move relatively freely. Unpowering a hydraulic circuit is much more complicated.

Jam in the gears is a bigger worry since unlike hydraulic actuators they cannot be floated.

@Jimmy yeah that's a possible failure mode, but a pretty remote one.

It doesn't matter. Single failure in flight controls is single failure, regardless of probability. Unless you want to have a word with the FAA

@Jimmy Direct drive is an option nowadays, no gearing between grip & motor.

That being said, for inceptors, the acceptable jam angle is 50%. So as long as you have a disconnect/override mechanism, you can design it to avoid a CAT scenario. For control surfaces (off topic), this probably involves splitting the surface and have two separate EMAs.

@Sean then use a motor that doesn't self-commutate, e.g. A stepper or brushless DC. It doesn't know how to move without the software telling it.

@JZYL It wouldn't be a single point of failure,there are two sidesticks-


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Isn't lift inverted when flying upside down?
How can an aircraft still continue to fly when it turns turtle or upside down in air? Is'nt it opposite of 'lift' principle?


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Why are an F-35’s missile rails angled outboard?
In this video of Marine ordnance crews loading an AIM-9X air-to-air missile onto its launch rail at the #11 weapons station of an F-35B, it’s clearly visible that the launch rail is mounted at an angle to the pylon.

Does anybody know what drove that decision to design this missile station in such a manner as opposed to placing the rail directly below the pylon as on conventional fighters e.g. the F-16, etc.?

Not only are they angled outwards, but they also point heavily downwards.

Is it young Tom Cruise loading a missile? :D

Yeah, it kinda does look like Tom Cruise from his days on The Legend set.

They are angled to give clearance for other wing mounted munitions. Comparatively speaking, the F-35 wings are rather short.
Here, showing missiles as well as 4x external bombs.

The munitions in the pic appear to be 500lb bomb bodies. But, 2,000 lb bomb are also applicable to those wing stations. Being fatter, they need more clearance.
(pic from https://defencyclopedia.com )

(pic from LockheedMartin, via The Weapons Zone - https://www.twz.com/wp-content/uploads/2023/03/24/Weapons-Stations-Capacity_v1.jpg)

Would be nice to have a pic that actually showed two missiles fitted to the same pylon...

@MikeB As I understand it, you don't ever have two missiles on the same pylon; the clearance needed is clearance for the missile on the next pylon over, and it has to be angled outwards to provide enough.

@Idran - There absolutely are single underwing pylons with 2x or 3x missile launcher rails. Possibly not applicable to the F-35, but they DO exist and are used.

They are angled outward merely to give enough clearance with its neighbour. Yes but then the question: why do they not simply hang perpendicularly down from the tip of the wing? That's because any external load that has to be attached to the wing needs to go through a rib. And the outmost rib in the F-35's wing is just where that AIM hangs (picture source):

As you can see, each wing has three main ribs (four counting the one at the interface with the fuselage) which is where the hard points of the weapons' launchers are located. The outmost couldn't be placed by the wingtips since on F-35 they are quite thin.

Which leads to the question "why are the ribs located where they are?"  The real answer is that the angled design is the best solution the team could find to the complex requirements and restrictions they were under.  Usually when there is a funny looking part like this there is a complex reason behind it.

I suspect the reason for having an air-to-air missile rail on a ventral bomb tack as opposed to a wingtip rail, similar to other fighters was based on radar, cross-section reasons. It’s easier to remove the bomb rack and apply a low RCS cover to the fitting on the bottom side as opposed to changing out the entire wing tip.

@RossMillikan: "Usually when there is a funny looking part like this there is a complex reason behind it". Actually is normally the other way around: when there is a part like that there was a lack of thorough reasoning and the need to find a funny looking solution  In this case it might be that the third hard point wasn't foreseen/requested at the beginning of the design phase or that some jettisoning requirement wasn't fulfilled during flying test and the quickest solution was to bend outward the launcher rail


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How does centre of pressure change with angle of attack?
I've been given the distance of centre of pressure from the leading edge with a certain angle of attack and was wondering if it's possible to calculate the new position when the angle of attack changes.

Closely related: http://aviation.stackexchange.com/questions/31878/what-is-the-aerodynamic-centre-and-how-does-it-relate-to-the-pitching-moment/31887#31887

This Wikipedia article explains that the movement of the center of pressure with changes in angle of attack depends on the airfoil shape.
In summary:

For a symmetric airfoil, as angle of attack and lift coefficient
change, the center of pressure does not move. It remains around the
quarter-chord point for angles of attack below the stalling angle of
attack.
For a conventionally cambered airfoil, the center of    pressure lies
a little behind the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves toward the rear.
For a reflex-cambered airfoil, the center of pressure lies a little ahead of the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves forward.

I do not have a simple expression that can be used to predict this movement of the center of pressure, but I suppose a computational fluid dynamics package can be used to model this for the specific airfoils used on the aircraft.

Its not a easy calculation. Even during our engineering we were told how it shifts but never any mathematical solution to it. But I have seen this being calculated on MATLAB.


text:
Is it possible for an airliner to cruise at engine full thrust?
What would happen if the pilot of a modern airliner like the boeing 747-800 or Airbus A380 left the throttle at full thrust at cruise altitude for an extended period of time e.g 4 hours if the aircraft had enough fuel to reach the next destination?

Full take-off thrust time is limited by the engine producer: bad things like overheating and meltdowns may happen. If you mean set the thrust to maximum allowable cruise setting: nothing much would happen other than consuming a lot more fuel than when using optimum cruise setting: fly fast enough, and the drag rises a lot without icrease in lift, due to compressibility effect. So the aircraft does not need to fly higher when going faster, it only burns more fuel.


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Can a turbofan maintain torque when spinning fast?
I assume turbofan fan rpm could be increased only when:

Using most modern jet engines (Airbus A380 and the Boeing B747-800)
Using a magnetic gearbox which can handle more torque dor the same weight
Fan and compressor blades are reinforced
Design muffles and silences the fan sonic boom
Engine is designed to prevent a flame out.

Assuming the problems above are solved, and one was able to redesign the fan and compressor blades to be efficient at 10 times their current rpm, without changing the power rating:

Would the engine have enough torque and power to spin the fan at cruise altitude?
What would be the effect on thrust?

I'm not clear on what your exact question here is, but it's actually more efficient to run the fan at a lower RPM than the low-pressure compressor and its associated turbine stages. This is why the geared turbofan exists. The most notable of this is probably the P&W PW1000G.

Related (about optimal fan/propeller speed): Is it possible to drive a turboprop directly from a jet engine without a gearbox?

An initial thought is that at 10X the RPM, it is likely that the blades would be well into Mach numbers, which would have a negative effect on power requirements (that is substantially more torque in particular) to spin the fan, and more importantly the fan would not be effective at those speeds.  There would likely be blade damage as well from the loading.
However this is a rather hypothetical question, where if an engine were developed to do this, there would be other trades to be made in the design of an engine. Changing just one part of a system such as a jet engine, usually does not favorably alter the overall performance.

Most high-bypass turbo fans have the tip speed just slightly supersonic at top speed.  Maybe mach 1.1, maybe a little higher.  At 10x speed, the blades would be Mach 11!

Not to mention that the pitch of the blades would be far too much, even if they didn't melt, which they would.

Turbofans don't need to spin faster, they need to spin slower to limit fan tip speed:

Compressibility drag is not a good item to spend fuel on.
Blade tension is a quadratic function of rotational speed. At 10x spinning speed, blade tension is 100 times higher. The blade root would have to be 100 times thicker at current technoloy.

Magnetic gears are made of permanent magnets, heavy clumps of magnetic iron: not a good combination with spinning 10x as fast. Mechanical gearboxes are used to gear down the propellers in turboprop engines, and geared turbofans use mechanical planetary gearing to reduce fan blade speed.
Perhaps magnetic gearboxes will find their way into turbine aero engines in the future, when the technology is fully mature, but for now mechanical gearing does the job. They reduce prop & fan speed though, not upgear them 10 times.


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Do airliners use light alloy wheels, like cars do?
Do large and small airliners - up to jumbos like the Boeing 747 and Airbus A380 -
 use light alloy wheels in their landing gear to reduce weight?
If not, why not? Are there reasons unrelated to weight? Do extreme temperatures and rapid temperature changes affect the material in a way that could pose a danger to the aircraft?

What alloy? Carbon steel is alloy, too. Safe too say all metal used for any structures is one form of alloy or another.

As opposed steel which I deem much heavier and not fuel efficient.  The extra weight could be an extra 150 passengers

@securitydude5 Steel is an alloy to begin with. I don't know what exactly "alloy wheels" are, but when it comes to cars, that's a marketing term, not really an accurate description of what they're made of.

All non-elemental metals are alloys.  Alloy wheels, I think, originally just referred to wheels that were not chromed or ordinary steel; chrome requires a lot of upkeep, especially on wheels.  Other ideas where they were lighter than steel wheels and less likely to 'freeze' to the rotor (which is not true depending on the alloy), but still could have that shiny look of chromed wheels.  Mostly marketing like @DanieleProcida said.

@securitydude5: 150 passengers at a modest 65 kg each would be almost 10,000 kg. Assuming you mean aluminium alloy, density about 2700 kg/m³, vs steel, 7850 kg/m³, that means that you think that some aircraft have $ 10000 \times \frac {7850}{2700} = 29000 ; kg $ of wheels. Where did you get those numbers from?

@Transistor: Passenger weight has gone up and is now above 80kg for short- and 100kg on long-range flights. The larger baggage allowance makes up most of the difference, but also more food that needs to be loaded on longer flights.

According to Wikipedia the term  "alloy wheels" is usually used for wheels made of aluminum or magnesium alloy.

@Transistor I assume they carry 10000kg of wheels

Lufthansa says that a 747-400 wheel rim weighs 74.4 kg. It has 18 wheels
[1x2]+[4x4] so that makes 1339 kg. Using Peter Kampf's figure of 100 kg/passenger all the wheels on a 747 weigh about 13 passengers. If you could reduce the weight of the wheels by 50% (and this is unlikely) you could accomodate six more passengers (without seats) not 150 as you thought.

@user3528438: You are right to say everything not pure can be an alloy, but the question is actually about light alloys, and for the purpose of reducing weight: "light alloy wheels in their landing gear to reduce weight?" To me this seems a good question, +1.

I believe the wheels are mostly aluminum ( alloys, high strength- heat treated , stronger than automotive types)  However most of the rest of the gear is high strength steels ; such as 4330 at 200,000 + psi strength level.

Here's a description of small aircraft wheels:

Available in 4", 5" and 6", these wheel & brake assemblies are cast from 535.2 aluminum alloy for superior strength and corrosion resistance.

And some info on 535.2 AL alloy
http://www.matweb.com/search/datasheettext.aspx?matguid=9347211fc1e1476988dfee51d8241c3c

"Light alloys" would also include magnesium, which has been used in aircraft construction.  These days, one might imagine a carbon composite.
Light alloys tend to lose strength at lower temperatures than steel, and are easier to bend.  Magnesium and aluminum will support combustion.
Many places where lighter materials are beneficial,
but wheel rims may not be one of them due to close proximity to heating from the brakes and stresses from
landing, especially in larger aircraft.

While I've no experience of larger aircraft, the wheel rims on the Piper Cherokee are certainly a non-iron alloy.  Presumably an aluminium alloy of some sort, but I never had a chemical analysis done :-)

They are coming into use on 18 wheelers as well.  My trust in steel may be old fashioned, would like to see cost and strength per pound analysis.  Aerospace applications certainly favor lower weight.


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Would winglets add fuel efficiency on a Concorde?
Would adding winglets to a Concorde have a had a positive impact on its performance and fuel efficiency in retrospect, considering the technology was not widespread or developed at the time these machines were flying and would that at all have reduced/increased its sonic boom?

The answer is no and the airplane in question is intentionally designed this way.
Standard sweptback wings produce the characteristic vortices st the wingtips.  The concentration of these vortices at this point in combination with little lift being produced by the vortices makes a singlet an effective feature to reduce induced drag.  Delta wings on the other hand produce vortices along the entire length of the wing, particularly at low speeds and high angles of attack.  Concorde designers took this into account in order to produce better low speed handling characteristics as well as the olgive delta wing provides a very clean high speed wing.  The wing was one of the most heavily researched and planned features of the jet during development.
The upshot of which is that adding winglets onto a Concorde not only is fairly ineffective way to reduce wingtip vortices and induced drag but impinges upon low speed flight capabilities, requiring greater takeoff and landing rolls and high approach AoA.

No they would not.
Winglet technology for supersonic aircraft was already a known factor when Concorde was designed. The XA70 Valkyrie Mach 3 bomber prototype first flew in 1964 and had folding down wingtips: extended during subsonic flight, folded downwards like winglets during high speed supersonic flight, for increasing lift by riding the shock waves. The Concorde designers had their own elegant solution to merge high- and low speed requirements in the wing design, in which winglets had no place.
Image source
The sonic boom shocks form at every point the airflow hits the aircraft structure, limiting the magnitude on the ground is more a matter of spreading the shock wave out.
The magnitude of the sonic boom depends mainly upon:

Length of the aircraft, the shorter the louder.
speed of the aircraft, the closer to the speed of sound the louder.
Altitude of the aircraft, the lower the louder.

None of these factors are influenced by the addition of wingtips.

Also the cross sectional area of the airplane. The more abrupt the change in area; the louder.


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At what altitude after takeoff is thrust reduced for airliners?
When is thrust, after take off reduced for jumbos and smaller airliners?
Is it any different for jumbos and smaller airliner aircraft?


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Can the bleed air for deicing the wings of the aircraft be switched on and off for jumbos?
Considering the large surface areas of the wings of the Boeing 747 and Airbus A380, can the bleed air for deicing the wings be switched on and off as needed and if so, is that automatic and where are the sensors to control this (on which parts and why).

For the reader unfamiliar with aircraft systems I’d like to comment that on most airliners I am familiar with, only the wing leading edge (and engine inlets) are heated with bleed air for anti-ice purposes, but not the whole wing. Even the leading edge might only be „anti-iced“ partially. (Comment triggered by reference to wing surface area in original question)


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Are all US fighter/combat aircraft constantly armed, even just in training?
I remember hearing once upon a time that all US fighter/combat aircraft constantly armed, even just in training. If I recall correctly, it's because the pilots need to be ready at a moment's notice.
Is this true?

No, for example the F-15 and F-16's are often flown for airshows/sporting events without being armed. Some may require ballast in the place of the arms though, I think the A-10 requires it.

thank you. i remember hearing that long ago and my wandering mind gets the best of me

@Ron Beyer: If a plane requires ballast, what happens in combat after it has expended all its munitions?

I meant if the cannon was removed.

Not only is the answer no, but this was a specific issue during the 9/11 response where some of the responding fighters were unarmed.

Bit late but see this story: https://www.washingtonpost.com/local/f-16-pilot-was-ready-to-give-her-life-on-sept-11/2015/09/06/7c8cddbc-d8ce-11e0-9dca-a4d231dfde50_story.html

No, if by "armed" you mean "capable of expending ordinance". ALl fighters with guns always have the guns, (it's not possible or necessary  to remove them for flights when they are not needed) and, for weight and balance issues, often they still carry gun ammunition, but unless there is a real or training requirement to fire the gun, it is will be safetied from the gun bay where the aircrew is not able to fire it.

As a general rule, unless you are going to use ordnance e.g. training, alert status, or war, you are not going to have it loaded on the jet.  It's just another risk to personnel or equipment out on the line, in hangars, etc.  Aircraft returning with live ordnance are disarmed and unloaded after shutdown and the weapons defused and returned to the bomb farms on base or magazines aboard ship.


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Why do some flights make turns shortly after takeoff?
I have seen that flights will make a turn, after traveling some large distance (say after some kilometers), but that can be done before.

Why not flying directly like in 2?
I am not expecting a passenger flight to do like fighter jets and perform nearly vertical take-offs, or some other manoeuvrers.
Are these flights restricted to do so, or is there any reason to behave so? Or did I misunderstand something?

@min, As mentioned in the image, why flights go some long and taking the turn? Instead that turn,could be taken before.so it will save some 'x kms', and also all flights can follow the same path while travelling for the same destination.  So is there any sort of rules and regulations they are having. Ex: You must have noticed this if u are inside the flight. They will fly to some distance, and they will make a small turn and while approaching the destination they will make a small turn. That turn could be made before and it will be the shortest path. This is my question..

If the question is Why an aircraft doesn't turn as soon as possible and at once towards its destination, to fly the shortest route? (better drawing), then I think @Federico 's answer is good. Is there something missing?

Think about how "inefficient" your car route might look to someone who doesn't know you have to drive it on roads :)

Here"s a good map of an airport with some arrivals and departures like you describe:  They're taking very systematic but inefficient routes for reasons like noise abatement: https://si.wsj.net/public/resources/images/BN-LF056_MIDSEA_P_20151111122256.jpg

Possible duplicate of Why do pilots use airways instead of just "flying direct" every time?

@NANDA - I hope the edits have all been in the spirit of your original question. The answers are all good, but I think they may have biased the edits (including mine) to your original question. Come on back and give some feedback to ensure we're answering what you're asking, and if one of the answers answers the question best for you, feel free to click the check mark next to it. If not, please clarify and we'll try a different approach.

Sometimes the "most efficient" route would cause you to fly too close to another aircraft, or land too soon after another aircraft. In those cases extra distance might be put in the aircraft's path to make it arrive somewhere a little later, when it's safer. Unlike a car, the airplane cannot always slow down as much as needed to avoid getting somewhere sooner than it should. The airplane also cannot make really sharp turns while still flying normally.

It is mostly standardized procedures.
I take as example Amsterdam airport (AMS), but the following is applicable to most, if not all, major commercial airports.
Let's look at the departure charts, in particular this one:

as you can see, if an airplane is departing via that runway, it MUST follow one of the two specified paths to exit the airspace of the airport through the "ANDIK" waypoint. It has different paths for the other exit waypoints, but they are similarly defined and limited in number.
In the link you will find similar charts for each of the runways.
Within restrictions due to factors like terrain, noise abatement over populated areas (as Dan's mentions in his answer), areas restricted due to security and safety (over city centres, government and military installations, nuclear power plants and such) or used for other purposes (military operations, space launch and such), these routes are defined so they don't intersect (much).
This ensures arriving and departing aircraft don't come close to each other, which greatly reduces the risk of collision and allows responsibility for different routes to be split among several controllers who can each handle their assigned routes mostly independently of the others.
Weather conditions and other factors will dictate which runways are used, but the runway will dictate how the airplane will exit the airport's airspace, after the appropriate exit waypoint has been selected (you generally would not use a waypoint on the north side if you have to go south).

So, to summarize:

you have a limited amount of exit waypoints
you have a limited amount of runways
weather will restrict your choice (well, the airport's tower will do this for you) of runway
your destination will restrict your choice of exit waypoint
for each runway-waypoint pair you will have one or two possible routes

This results in the kind of behaviour you have observed.

Well, the most important property of the procedures is that the paths don't intersect (too much), so the responsibility for the aircraft can be split between multiple controllers and each can work, within the assigned routes, mostly independently of the others.

Another reason might be the Earth's curvature, making routes near the poles appear as big curves going away from Equator's line in sites like flighradar24. But these need a lot more than some kilometers to be visible...

And even with just one controller if the paths don't intersect (too much), the controller can be confident that the arriving and departing traffic won't come anywhere close to each other when using the standard routes, significantly reducing their workload and risk of collision.

@JanHudec sound reasonable to me, feel free to add it to the answer! thanks!

The 2 particular routes shown are west and south of Amsterdam, definitely noise-related. The topological part here is that the climb from Pampus is over open water (IJsselmeer), and is most of the climb after Spijkerboor.

I saw a related question that presented another routing issue: restricted areas.

@Federico, added.

Aircraft are routed based on all manner of different things. Just off the top of my head, here are some of the more common reasons:

Standardised routing. It's much easier for controllers to manage aircraft if everyone is following a similar route, and so there are generic routes defined. This is especially true in and out of airports - imagine if dozens of planes were simply arriving in any direction they like, it would be very chaotic to deal with.
Noise Abatement. Many areas have noise abatement procedures, where aircraft are either restricted from flying over or the number or flights is limited. It's not uncommon for aircraft to have to fly around certain places.
Weather Avoidance. For comfort and safety, aircraft will sometimes be routed around certain types of weather.

This isn't an answer, just an addition to @federico's answer.
The following image shows departing aircraft from international airports near my location, Düsseldorf (red) and Cologne (blue). The data was recorded over 24h from flightradar24 and put on a map together with some beacons. The dotted lines indicate the angles mentioned below.

Looking into the departure charts for Düsseldorf, one finds for take-offs to south-west this, in layman’s words:

Turn hard right and fly away from NOR at 0°
Turn right to LMA (Roughly, there are more points not shown in the map,  and more than one route), then depending on destination turn left to 203° or 209°.
Turn left and fly to NOR at 174°, then turn left to GMH at 86°

Finally, there's a chart showing all this together, though this is more about noise:

For cologne it's obvious that there are similar rules. It's also clear that the flights from Düsseldorf to south-east are guided around Cologne by flying a little towards GMH first.
So, not an answer, just to show that aircraft fly as they are intended to do, though there are a few exemptions.

You could have edited Federico's answer, but I think yours does a pretty good job of standing on its own.

Just like you can't drive your car straight from point A to point B because there might not be a direct road between the points, aircraft can't necessarily fly from point A to point B because there might not be airways that directly connect the points.
Also, most traffic between major airports will follows established procedures. These are either Standard Information Departure (SID) - for flights departing or Standard Terminal Arrival Route(s) (STAR or STARS), for flights arriving.
These standard departure and arrivals procedures are put in place based on the geography, weather or other restrictions at or near the airport and don't have to coincide with the flight's arrival or departure direction.

Not everyone (especially one asking a question like this) is familiar with SID and STARS. Your answer would be improved by defining those within your answer or including links to Wiki, Skybrary or other sources of definitions. (Sure, someone could Google them, but remember, we're here to answer questions, not create more work!)

@FreeMan - fixed.

Thanks, @BurhanKhalid, I could have done that as well, I was hoping our newer member would come back & take care of it. ;)

Just one clear answer why it is also done on short trips (so not depending on the earths curvature that much): Airplanes have the allowance to fly on a flight level (FL), given in feet / 100 AND refering to an imaginary surface level where the standard pressure of 101325Pa is located. So FL 130 is 13000 feet above the level with 101325Pa ambient pressure.
Some turns are only allowed at that FL to avoid collisions with other airplanes.


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What is the applicable regulation for flying in a residential area?
What are the laws for flight in a residential area. Can I just fly around the neighborhood or do I have to have a flight plan? I have my own strip.
I have had some noise complaints about just flying back and forth around the neighborhood

Welcome! In which country?

I doubt the people who are complaining are going to care whether or not you have a flight plan.

14 CFR 91.119 says 1,000 feet.

As well as which country, what exactly are you flying?

As @GregHewgill said, a flight plan does not entitle you to break noise abatement problems. They don't notify people in the area of flight plans about noise. This really depends on where you are located, but as long as you abide by minimum altitude rules and airspace restrictions, nothing (should) prohibit you from tooling around the area without a flight plan.

[nitpicker] you'll find it quite difficult to fly in a residential area, you'll have more luck flying above it [/nitpicker]

@Federico Of course that is why there is a lot of noise complaints - because of the explosions!

This sounds more like it's about RC airplane, or quadcopter or something. In which case you quite possibly fly in a residential area

I am going to assume you are asking about regulations as they pertain to the U.S. and the FAA.
abelenky is on the right path. 14 CFR 91.119 states that that over a congested area, i.e. your neighborhood area, you must stay at least 1,000 feet AGL.  The only exceptions would be of course for purposes of takeoff, landing, and remaining in the traffic pattern, if the traffic pattern is set at less than 1,000 feet AGL.
As far as having a flight plan goes, as long as the flight remains under VFR conditions and does not cross into the Washington DC FRZ/SFRA areas or cross the ADIZ you are under no regulatory requirement to file a flight plan.
Though a flight plan is still highly recommended any time you are flying away from the vicinity of the airport (generally considered more than 25nm) or no one else knows you are flying.
As far as the noise complaints, I have a few recommendations

Use a lower power setting IF POSSIBLE.
   Using a lower power setting will help keep down the noise.
Choose to stay at a higher altitude rather than at the minimum 1,000 feet AGL
Try to fly out a little further and give some time between your passes over the neighborhood.
Offer to take some of those neighbors on a flight! Often times once people with complaints about aviation will stop complaining once they see how much fun it is.

Hope this helps!


text:
What are the FAA sport-pilot self-certification standards?
Consider a hypothetical pilot who knows they have a medical condition which the FAA considers disqualifying (under the standard medical qualification standards). Is that pilot permitted to operate under sport-pilot privileges if they do not believe their condition interferes with their ability to safely perform their sport piloting duties? Must that pilot consult with a private physician? If so, must the physician offer some sort of approval?
The FAA has a similar question on the FAQ, but doesn't seem to answer it fully. They "suggest" consultation with a physician. Does that suggestion indicate a pilot who does not do so is in violation of a FAR?
edit: This question is concerning operation of a powered airplane.

Unless the pilot has had their certificate revoked or suspended by the FAA for their medical condition or has failed an application for a medical certificate1, they would probably be fine after seeing a physician. FAR 61.23(c)(2) states that sport pilots using a driver's license to satisfy medical requirements must:

(ii) Have been found eligible for the issuance of at least a third-class airman medical certificate at the time of his or her most recent application (if the person has applied for a medical certificate);
(iii) Not have had his or her most recently issued medical certificate (if the person has held a medical certificate) suspended or revoked or most recent Authorization for a Special Issuance of a Medical Certificate withdrawn; and
(iv) Not know or have reason to know of any medical condition that would make that person unable to operate a light-sport aircraft in a safe manner.

If the holder has a valid US driver's license, it would (presumably) be taken upon the certificate holder to have "reason to know" by virtue of having a checkup with a physician to check that this condition does not affect their ability to fly safely, especially if the person involved was in any sort of doubt as to their medical condition.
However, if they have had a checkup with a physician that finds no particular issues, and that condition does not affect the validity of their driver's license, they should be fine.
1: By section (ii), the pilot must still have a medical test and pass for at least a Class 3 medical certificate, if the FAA has revoked or found unsatisfactory their previous medical under a Class 1 or Class 2 certificate.


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How is flame stabilisation carried out?
How is flame stabilization done in a jet engine combustion chamber?
What are the various ways of doing this?
What are the challenges/ problems faced?

After reading several documents related to flame stabilization, I don't think aerodynamics is the proper tag here

Related: How is combustion flame maintained in the combustion chamber after igniters are switched off? - The keyword here is "flame holder".

As usual, it is a combination of measures:

Flow speed at the start of the combustion chamber is the lowest in the whole engine, in the order of 30 m/s.
High fuel pressure and many small fuel injector nozzles, such that the mean fuel droplet size is kept as small as possible
Flame holders cause a pocket of stagnated, burning flow which helps to ignite the fuel-air mixture
The combustion chamber is long enough to allow most of the combustion to happen inside, such that radiated heat from the burning gas ignites the fuel-air mixture upstream.
In marginal conditions the ignitors are switched on to help speed up the ignition.
Control of parameters, such that fuel starvation by rapid throttle changes can be avoided. Examples are fuel control units, where a centrifugal feedback valve would control fuel flow depending on the engine's rotational speed, or electronic control (FADEC).

Much can be done by running the engine such that the risk of flameout is minimized. The operational measures to ensure a stable flame would be:

Avoid fuel starvation (empty tank, fuel pump failure, clogged pipes). This one is obvious, but I need to include it for the nitpickers.
Avoid too low pressure for rapid combustion: Pressure speeds up the chemical reaction, and if the aircraft flies high and/or throttles down, the lowered pressure in the combustion chamber might cause a flame-out. High-altitude jet engines have longer combustion chambers as a precaution.
A compressor surge or disturbed inlet air flow can cause a sudden pressure loss in the combustion chamber and a consequent flame-out, the latter especially in supersonic fighters with their long intakes and high angle-of-attack capabilities.
Avoid sudden cooling of the air inside the engine, e.g. by heavy rain. The additional water extracts energy when it evaporates and causes a temperature drop in the combustion chamber which can lead to a flame-out of a throttled-down engine. Another possibility is too much fuel which has been ingested by the intake in a botched aerial refueling attempt.
Avoid clogging of the inside of the engine by ingested dust, like gun smoke or volcanic ash.